The objective of this research on sympathetic ganglia is to describe the ultrastructure of B and C preganglionic nerve terminals at rest and during dynamic functional states such as synaptic depression, recovery, facilitation and post-tetanic potentiation. Special attention will be given to synaptic vesicle number and distribution near presynaptic release sites. In addition, the mechanism of membrane retrieval and synaptic vesicle reformation during transmitter secretion will be studied. The preparation used will be the IX caudal paravertebral sympathetic ganglion of the bullfrog. Methods will include post-ganglionic recordings using suction electrodes, conventional electron microscopy, extracellular tracer techniques using horseradish peroxidase or dextran, rapid-freezing, freeze-substitution and morphometric electron microscopic analysis. It is hoped that this project will provide a cytological basis for a better understanding of synaptic function.